Air springs have been used for motor vehicles and various machines and other equipment for a number of years. The springs are designed to support a suspension load such as a vehicle. The air spring usually consists of a flexible elastomeric reinforced airsleeve that extends between a pair of end members. The airsleeve is attached to end members to form a pressurized chamber therein. The end members mount the air spring on spaced components or parts of the vehicle or equipment on which the air spring is to be mounted. The internal pressurized gas, usually air, absorbs most of the motion impressed upon or experienced by one of the spaced end members. The end members move inwards and towards each other when the spring is in jounce and away and outwards from each other when the spring is in rebound. The design height of the air spring is a nominal position of the spring when the spring is in neither jounce nor rebound.
There have been two basic designs of air springs: a rolling lobe air spring, as seen in U.S. Pat. Nos. 3,043,582 and 5,954,316; and a bellows type air spring, as seen in U.S. Pat. Nos. 2,999,681 and 3,084,952. In a rolling lobe-type air spring, the airsleeve is a single circular-shaped sleeve secured at both ends. During jounce, the airsleeve rolls down the sides of a piston support. In a bellows-type air spring, the multiple meniscus-shaped portions of the airsleeve extend out radially as the spring is in jounce.
Airsleeves have a rubber innerliner, two plies of rubber coated cord fabric, and a rubber cover. These sleeves see their greatest commercial usage in the automotive helper spring market by being mounted as air springs on shock absorbers and struts. Other uses include truck cab suspension springs, truck driver seat springs, automobile air springs, and a variety of industrial air springs.
The plies of cord fabric are contained within a reinforcement layer, which along with the cord fabric includes an elastomeric base, or plycoat, made from a rubber compound. The reinforcement layer may be provided from a plurality of different types of materials. The rubber compound of the plycoat is selected from among elastomers conventionally used in manufacturing airsleeves, and blends of such elastomers. Also typically included in the rubber compound are various additives.
In the manufacture of fabric-reinforced, molded rubber articles such as airsleeves, it is desirable to obtain strong adhesion between the fabric and the rubber, and also high resistance to deterioration of the bond with flexing of the structure.
The adhesion of the plycoat to the cover is essential for acceptable performance of composites in applications such as airsleeves. Further, the adhesion of the reinforcing cord to the plycoat is essential for field performance, especially for its high stress tolerance. An adhesive based on a styrene-butadiene rubber (SBR) latex, a vinylpyridine/styrene/butadiene terpolymer latex, and a resorcinol/formaldehyde condensate is typically used to adhere the cord to the plycoat.
The rubber compounds used in the air spring cover are dictated largely by the operating environment to which the air spring is exposed. For airsleeves exposed to a high temperature operating environment, up to about 115° C., an epichlorohydrin rubber (ECO) based compound may be used for the cover, along with a sulfur-cured natural rubber plycoat compound. While this combination of an ECO cover with a sulfur-cured natural rubber plycoat provides adequate service life in some applications, automotive specifications require increasingly better performance from airsleeves.